Scientists have identified a method to create multiple copies of quantum information by encrypting them with a one-time decryption key, sidestepping the no-cloning theorem. This approach, developed by Achim Kempf and colleagues at the University of Waterloo, was tested on an IBM quantum processor. The technique could enhance redundancy in quantum computing and storage systems.
The no-cloning theorem, established in the 1980s, holds that quantum states cannot be duplicated without destroying their properties, a principle foundational to quantum encryption and security protocols.
Achim Kempf at the University of Waterloo in Canada, along with his team, has demonstrated a workaround: cloning quantum systems by encrypting the information and pairing it with a single-use decryption key. "You can make a lot of copies and generate redundancy in this way, but you have to encrypt the copies, and the decryption key can only be used once," Kempf explained. This ensures compatibility with the theorem, as only one unencrypted, readable copy exists at a time.
The idea emerged from research into quantum Wi-Fi or radio systems, where multiple receivers would otherwise violate the theorem by receiving identical quantum data. The team found that quantum noise effectively encrypts the information, which can be intentionally leveraged and reversed. After theoretical proof, they implemented the protocol on an IBM Heron 156-qubit quantum processor, producing hundreds of encrypted qubit clones. "In fact, we ran out of real estate on the IBM processor. It holds only 156 qubits but we estimated that we can do more than 1000 encrypted clones before the [errors] make us stop," Kempf noted. The method shows resilience to noise and errors common in current quantum hardware.
Potential applications include quantum cloud storage, akin to classical systems like Dropbox, which replicate data across multiple sites for reliability. "If you send a file to Dropbox, it will save your data at least three times in three different computers that are geographically separated, so that if one is hit by fire, the other one by a flood, there’s a fair chance the third one survives," Kempf said. "It used to be thought you can’t do that with quantum information, because you can’t clone it. But what we showed is that you can do it."
Aleks Kissinger at the University of Oxford described it as "an interesting quantum cryptographic protocol" useful for redundancy in quantum communication. He clarified, "It’s not so much cloning as a kind of spreading the [quantum] state to lots of other parties, in such a way that any one of those parties could later get it back." Kempf concurred: "It’s not cloning. It’s encrypted cloning. That’s just a refinement of the no-cloning theorem."
The findings appear in Physical Review Letters (DOI: 10.1103/y4y1-1ll6) and arXiv (arXiv:2602.10695).